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Re: 10si or 12si GM Alternators

I've long suspected that the "sense" wire pin (pin #2 on the slip on plug) has an internal connection to the output terminal of the alternator. The connection would have to have more resistance that a direct short, lets say 100 ohms just for laughs. That way if a real sense wire was connected to pin #2 the sense wire voltage would be passed to the fairly high impedance voltage regulator sense input in the alternator. without regard to the voltage on the terminal. But if no wire were connected to pin 2, the voltage from the output terminal would find its way through the 100 ohms (or whatever) of the internal resistance and into the voltage regulator.

Question: What do you think?

Question 2: Could I test my theory by ...
... A. Removing the sense wire from my own 10si 3 wire alternator, start the truck and see what happens?
... B. Removing the sense wire and the output wire, then measuring resistance between the 2 points on the alternator?

What are you actually trying to figure out? This sounds like step N in a process.

An internet friend is installing a wiring harness advertised as being for a 1 wire alternator, but comes with the 2 pin plug that has wires for both the pins. PIN 1 hooks to the ACC connection on the ignition switch. Pin 2 wire is a short connection to the output stud of the alternator, a 12si, 94 amp model.

His question to me was why does my 1 wire alternator have 3 wires?

Mostly because most of the "one wire" vendors share a situation with Pinnochio- - - -one of these days they're going to have a long nose. In other words, they're lying. Some (not all)"one wire" alternators have different regulator internal wiring so those terminals on the perimeter of the alternator aren't needed. They usually have a rubber plug installed in the rectangular slot on the perimeter of the housing. If you've got one of them, just connect the heavy gauge charge lead and drive on. If the two blade terminals are exposed, wire the thing the way GM engineered it.
Jerry